Granular polyvinyl resins



" Patented Apr. 24, 1951 UNITED STATES PATENTQFFICE 2,550,503 v GRANULAR POLYVINYL misn'vs Norris Turnbull, Grand Island, N. Y; assigli or to V E. L'du Pont de Nemours & Company, Wilmington',Del., a corporationof Delaware No Drawing. Application July 1, 1947,

' Serial No. 758,4 8 3 16 Claims.

TI'h'is' invention relates to the production of polyvinyl resins in granular form and more particularly to a means for preventing coalescence of the granules. I

.Thermoplastic vinyl resins such. as polyvinyl.

acetate may be produced in granular form by various methods. One form is head. polyvinyl acetate, consisting of smooth spherical particles which may be made in various sizes. Another form consists of small particles of irregular shape. Such granular material is convenient to handle'in various operations, suchas measuringand dissolving. However, since polyvinyl acetate is thermoplastic and exhibits considerable cold flow at ordinary temperatures, it often is necessary to refrigerate this material during storage to prevent coalescence of the particles to (01. zeo zv) large masses which are then difficult to dissolve.

Such refrigeration is costly and undesirable.

It has been found advanba eo'usto prepare beads or granules of polyvinyl acetate by polye merizing the monomer dispersedjin water containing a small amount of surface active compound as a dispersingagent; These beads can" be prepared with a high a degree ofnuniformity which is of considerable. importance in solution.

operations.

The wet 'beads obtained, afterrpolymerization generally are centrifuged to removea large proportion 'of the external water and arethen dried, with warm air. In order to dry the beads at a I reasonable rate, it is necessary to use a drying temperature of 40 80' C. Under these conditions, unlubricated beads will agglomerate to form large lumps. The dried heads will also agglomerate onstorage at ordinary temperatures injthe absence of a lubricant- Magnesiumstearate and ther lubricants applied to the granules have. proved: to be very effective in preventing agglomeration of poly vinyl acetate in plant practice, but they are insoluble in the organic solvents commonlyused-- for dissolving the polymer and give ble'f cloud to the resulting solutions. t A V I agent is desired which is soluble in organicv solvents commonly used for dissolving polyvinyl an undesiraacetate, such as benzene, acetone, ethanol, meth anol and the like, and which will prevent the agglomeration of the. polyvinyl acetate particles during processing and storage.

The problem of agglomeration is not confined to polyvinyl acetate but occurs likewise with polymers of other vinyl esters of carboxylic acids and copolymers of such vinyl estersflvhich have thermoplastic properties. similar to those of polya division of the granular resin, as

vinyl acetate. Such thermoplasticproperties are generally shared byth'e various polymers of'e s-" ters of carboi'c'ylic acids, for example, polymers of vinyl formate, propionate, benzoate, naphthoate and stearate. The thermoplastic properties of vinyl ester copolymers depend upon thepro? portion of the vinyl ester" in the'cop olymer, the" nature of the copolymerized constituent or con stituents and the degree of polymerization. Generally, those copolymers of vinyl acetate orother vinyl ester inwhich the vinyl ester is. the pre; ponderant constituent have thermoplastic'prop j erties which tend to cause,v agglomeration of granules. For example, copolymers ofvinyl ace- 1 tate with vinyl chloride containing upwards of by weight of the acetate generally are sufflc'iently thermoplastic to cause agglomeration during storage. j

an'improved means forpreventing agglomera A, tion of granular polymers and copolymers r: vinyl esters of carboxylic acid. A'further object 7 is an anti-agglomeration agent which in commonly-used polyvinyl Other objects will be hereinafter apparent.

The above objects may be attained in accordance with the present invention by applying to. the granular thermoplastic polymers and copolymers of vinyl esters of carboxylic acids, and in particular, polyvinyl acetate, a coating or layer of rosin or a productiof rosin, including abietic. acid, hydrogenated rosin and polymerized resin.

The ordinary rosin of commerce'which is a mixture of diterpenecarboxylic acids, chiefly abietic acid, is efiective' as an antiagglomerant. Re fined grades of rosin and the so-called poly.

meri'zed rosins are still more effective. Other types of processed rosins, e. g. hydrogenated ros ins also may be usedwith satisfactory results Abietic acid also is effective. Either crude or refined forms of rosin or; these rosinproducts may be used.

p 'The rosin may be. applied to the granular vinyl resin in any desired rnanner, so as to coat the: surfaces, of the granules therewith, and relatively small amounts are required- An amount sufiicient jto give thegenerally glossy, surface of the: vinyl resin granules asomewhat dull appearance, is generally .very. effective. The amount redepending on the state of sulp-- the amountof.

quired. will vary surface to be coated varies inverselyjwith granule" size. galenerally less, than ;5.%.;-by weightof rosin'will suffice and'in most cases about 0.5 to

' An objector the: present invention is to provide,

is soluble ester solvents.

is satisfactory. The vinyl resin particles may be either dry, or wet with water or other non-solvent, when the rosin is applied. A convenient and preferred method is to mix: the g-nanular vinyl resin with finely powdered rosin, -.e. ;g.-,about 5,0

to 100 mesh size rosin. Another methodis to add the finely divided rosin to a slurry. or dispersion of the granular vinyl resin in water, removethe} water by centrifuging, filtration or other conven tional means of separation, and drying the -gran ular material. I may also apply the rosin in solution; in'a liquid which. dissolves rosin. but-is a. non-solvent for the vinyl-resin. For thispurpose, low-boiling hydrocarbonsrmay pe used as rosin solvents, for example, petroleum :ether, gasoline,hexanes heptanes, and the like. .-Such rosin solutions may be 'added-towet or dry granular vinyl resin .or .to .a slurry r dispersion thereof. 7

In ,-the manufacture of, granularor,bead-form polyvinyl acetate, :wherein the granularv material is producedbypolymerizationof an aqueous .dispersion of vinyl acetate inwater, I prefer .to. mix the powdered rosin with .the: wet,. .granu1ar polyvinyl acetate and thenevaporate oif-the-water byanyconventionaldrying operaticn. Thegranular .polymer removed. from rthe polymerization mamas. centrifu ed and washedwithwater-to remove dispersing agents and other contaminants which may result from; the polymerization operation. The, resulting. wet, .granular polymer, hayil an.averageparticlesiae .ofaboutOfi to 2mm,

;linch into the bottle.

' 4 dure described below, illustrate specific modes of practicing the invention and the results obtained:

Apparatus A rotary dryer was constructed using a 500 ml. bottle supported on small casters placed in a water bath. .Thbottle was --stoppered with a rubber stopper through the center of which a inch hollow shaft, 8 inches in length, extended A roller bearing was attached near the other end of the shaft to act as a support. The bottle and shaft were rotated by means ofa-beltandpulley arrangement attached 7 .to an airmotor; Agglass tube inserted through the;hollowshafttmnear the back end of the bottle. was used for conducting air through the dryer.

jThe. ofi-gaswas also vented through the hollow shaft. "Two 6 inch rods of glass or steel were 1 placedin the dryer to assist in mixing the beads.

is.thoroughly mixed .with about-0.5 .to 1% .by

weight .of {powdered rosinof about .50 .to 100 mesh size. .viarious conventional methodsandapparatus for.;mixin g solidmaterials maybeutilized for this. purpose, e., g. tumblingthe mixture ina rotating drum or other container. Themixed material isthendried at atemperature .of .40.;to 1.00? C..in a rotary. .dryer orotherf conventional drying equip- 4 ment, preferably tumbling. .orastirring: thematerial while drying. The drying temperature-must be-sufliciently low to maintain-thepolymer in-a substantially non-tacky condition. The polymer: granulestend to become tackyandstick together and to ,the dryer .walls at. lower temperatures whenwet, than when .dry. The initial-temperaturein the dryermay vary from'4i0 to C. without, undue sticking. .As .the drying operation pmceeds, the temperature can be. raised, to finish at- 6,0 to 100 C., substantially -Without sticking; Generally a rmaximumwdrying t mp rature t exceeding about 100 C. is satisfactory; but the maximum drying temperature .lwillvary, depending. on the specific grade of .polyvinyl acetate handled. The resulting rosin-coated granular material has a somewhat dull appearance, .as compared with untreated granular .polyvinyl acetate and is substantially-free of lumpsor other agglomerations. {It may be stored under ordinary storage and shipping conditions forlong periodsof time, substantially without. agglomeration or-adherence of the-granules. y

The experimental tests shown by the following examples, utilizingthe apparatus and proce- The temperature of the water bath, in which the dryer revolved, was controlled by injection of steam.

Procedure was attached to the drying assembly. The bot-* tle was submerged to about /3 of its diameter in the water bath which had an initial temperature varying *between 40 and '60" C. The temperature was controlled during the initial stages of the drying at a' value which would not allow sticking of the'beads to themselves or to the glass. (This wet-stage ofiers the'greatest=-difficulty in the drying op'erationand selection of the proper temperature for use with various lubricants requires considerable experience. After the major portionof the surface water isremoved, the temperature can normally be increased fairly rapidly to a maximum between 60 and 0., depending upon the lubricant and the type of vinyl resin.) The eifectiveness of the variousrosins tested was determined by noting the behavior .ofthe beads during the wet stage and by noting the temperature at which thebeads would begin to stick .to-

gether as 'the' temperature was gradually increased. (Inferior lubricants permit agglomeration of the beads during the wet stage ;at 40 C. or during the dry stage at temperatures below 50C.) "The dried beads were storedin a 4 5 C. oven for several days or weeks and ture for of the rosin to prevent. agglomeration during storage.

Solutions of the dried beads in .benzene, ethanol, and acetone were preparedfor examination as to clarity.

In Example 3 below, the polyvinyl acetate was a medium viscosity grade, having a viscosityof 70 centipoises. In the remaining examplesthe polyvinyl acetate was of the jlow-viscositytype, having viscosities of 3 to 1'7 centipoises, ,as indiat room temperasated. In each case, the viscosity noted is the one year, to determinethe effectiveness.

absence-.-

viscosity of a benzene solution containing 86.

carrying out the following.

equivalent to 0.6% by weight of the beads on a dry basis. The beads then exhibited an improvement in their flow'characteristios. They were then charged into the rotary dryer heated ina 41C. water bath and air was passed through the dryer. The temperature of thebath was raised gradually to 73 C. within 30, minutes. The granules-were then dry and free-flowing and did not agglomerate during storage at 45 C. for 7 days.

Example 2 Wetpolyvinyl acetate beads (5 cp. viscosity) containing 10% by weight'of water were mixed with finely ground refined rosin equivalent to 0.6% by weight of the beads on a dry basis. These coated beads exhibited good flow characteristics. The mixture was then charged into the rotary dryer in a 43 C. water bath and air was passed over the beads. The temperature of. the bath was raised to 73 C. during minutes and the charge was dry after a total of minutes. The granules were free-flowing, did not stick to the walls of the dryer and did not agglomerate during storage at 45 C. for 7 days.

Example 3 7 Due to the relatively high initial temperature (60 C.), some of the beads stuck to the dryer walls at the start of the run. However, at the end of the run, all of the granules were-freefiowing, discrete particles.

Example 4 Wet polyvinyl acetate beads (10 cp. viscosity) containing approximately 10% by weight of water were mixed with a refined rosin powder equivalent to 0.6% by weight on the dry basis. The coated granules, which exhibited improved flow characteristics, were charged into the rotary dryer heated at C. Within three minutes, the surface moisture had been reduced to the point that the granules were free-flowing like sand. raised within 57 minutes to 66 C. at which ten1- perature the beads were free-flowing. The resulting dry, granular polymer did not agglomerate during storage at C. for 7 days.

Example 5 ;.Wet polyvinyl acetate beads (17 cp. viscosity) were mixed with a powdered hydrogenated rosin equivalent to 0.6% by weight on the dry basis. The coated granules exhibited fair wet flow. The wet beads coated with the rosin were placed in the dryer heated in the bath at 37 C. The beads quickly stuck to the walls but gradually worked loose on further drying. At the end of 30 minutes, only a few of the granules adhered to the walls when the temperature of the heating bath Turbidity due entirely to polyvinyl acetate, as the lubricant is rea,ched=55, (3., and thedried-product;was free from agglomerates 1 Solutions of the lubricated, dried beads duced in the above examples (20% solids) were prepared and examined for-clarity with the following results:

20% Lubricated Polyvinyl Acetate-8011b E tionsin 10(EX8J11I)19 and Lubricant l I i Benzene Ethanol Acetone Example 1, Poly-Pale Clear Clear- Slightly tur-..

Resin. bid. Example 2, N Wood .do; "do; Do. 1115 Rosin.

Example3,AbieticAc-id. slibglatl ytur- 'do Do! Example 4,.Pexite M. Clear "do" D0, Resin. Example 5, Staybcllite do .l Slightlytur- ,Do. Resin. bid.

soluble in indicated solvents used in these tests.

FInrbidity due to'trace of lubricant which is .insolublein the indicated solvents. .I

Samples of thepolyvinyl acetate beads prepared in the above examples were stored in closed containers at room temperature, alongside samples of unlubricated polyvinyl acetate beads of the same viscosity grades. After one year storage the lubricated beads were free-flowin whereas the unlubricated beads were caked due to adherence of adjacent beads.

The herein described invention permits rapid drying of the wet granular polymer at relatively high temperatures without agglomeration or sticking to the walls of the dryer. It further produces a product which can be stored for long periods of time without agglomeration or caking. The product dissolves in the usual vinyl resin solvents to produce from slightly turbid to clear solutions.

I claim:

1. The process which comprises applying to the surfaces of a granular, thermoplastic polymerized vinyl carboxylate, in the proportion of 0.1 to 5% of the dry weight of said carboxylate, a rosin product selected from the group consisting of rosin, abietic acid, hydrogenated rosin and polymerized rosin.

2. In a process according to claim 1, coating wet polymerized vinyl carboxylate granules with the rosin product and then drying said granules.

3. In the manufacture of a granular,'thermoplastic polymer of a vinyl carboxylate by a process including polymerizing an aqueous .dis-

about 0.1 to 5% of its dry weight of a rosin product selected from the group consisting of rosin,

The temperature of the bath was abietic acid, hydrogenated rosin and polymerized resin and then drying said polymer at a temperature of 40 to 100 C.

4. The process of claim 1 in which the polymerized vinyl carboxylate is coated with rosin. 5. The process of claim 1 in which the poly- .merized vinyl carboxylate is coated with abietic acid.

6. The processor claim 1 in which the polymerized vinyl carboxylate is coated with hydrogenated rosin. 7. The process of claim 1 in which the polymerized carboxylate is coated with polymerized rosin. V

8. The process of claim 3 in which the said polymer is polyvinyl acetate and is coated with rosin.

sgsowsos 9, The process 101' claim '3 in which 1 the said polymer is polyvinyl acetate andis-coated with abitic a'cid.

10.-"Tl 1' rocess of ciai'm 3 in which the said polymer is polyvinyl acetate and is coated with hydrogenated rosin.

11. The process of'claim 3 in which the said polymer is polyvinyl acetateand is coated with polymerized rosin.

12. A composition of matter comprising granular; thermoplastic polymerized vinyl carboxylate, individual granules of which are coated with about'0.1 to 5% by weight of a'rosin product selected from the group consisting of rosin, abietic acid, hydrogenated rosin and polymerized rosin.

13. A composition of matter comprising granular polyvinyl acetate, individual granules of which are coated with about 0.1 to 5% by Weight of rosin.

14. A composition of mattercomprising granu lar polyvinyl acetate, individual granules of which are coated with about 0.1 to 5% by weight of abietic acid.

15. A composition of matter comprising granullar polyvinyl acetate, individual granules of which are coated with about 0.1 to 5% by weight of hydrogenated rosin.

16. A composition of matter comprising granular polyvinyl acetate, individual granules of which are coated with about 0.1 to 5% by weight of polymerized rosin;

NORRIS TURNBULL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. THE PROCESS WHICH COMPRISES APPLYING TO THE SURFACES OF A GRANULAR, THERMOPLASTIC POLYMERIZED VINYL CARBOXYLATE, IN THE PROPORTION OF 0.1 TO 5% OF THE DRY WEIGHT OF SAID CARBOXYLATE, A ROSIN PRODUCT SELECTED FROM THE GROUP CONSISTING OF ROSIN, ABIETIC ACID, HYDROGENATED ROSIN AND POLYMERIZED ROSIN. 